The present invention relates for a filter for aquariums.
One of such filters is disclosed, for example in U.S. Pat. No. 5,160,607 (German patent document DE-OS 40 13 324), and operates as an alternating lifting-lowering filter. This operation based in the known filter on the fact that each individual filter compartment has at least one overflow suction lift device which operates on the principle of the lift loop. Its inlet is located at the bottom side and therefore substantially at the height of the bottom of the filter compartment and its outlet opens downwardly toward the following filter compartment. The outlet of the overflow suction lift device opens in the lowermost filter compartment in a bottom chamber into the interior of the filter housing. With this design of the filter, a multi-stage operational sequence of the filtering is performed. The control of the cyclical lifting-lowering process is performed without special mechanically movable parts. For high filter outputs no limits is set. The known filter is suitable predominantly as an inner filter, while its use as an outer filter is also desirable. However, certain adjustments are needed for this application. For this purpose in the known filter an auxiliary chamber is formed which forms a throughgoing passage with individual tubular elements extending through the filter compartments located over one another to provide protection from a dry running of the pump. It is connected with an upper water supply of the filter so that when needed, unfiltered water flowing directly from the aquarium tank can be flow into the auxiliary chamber. The downwardly located outlet of this passage is controllable by a float-controlled valve device. It is located in a bottom chamber in the filter housing formed under the lowest filter compartment and placed in a motor-driven suction pump having a pressure side connected with the outlet pipe for supplying back to the aquarium tank the filtered water aspirated from the bottom chamber. The float-controlled valve device located inside the bottom chamber starts operating only when the water level in the bottom chamber, due to a defect or a faulty operation, is so low that there is the danger that the pump which aspirates water from the bottom chamber runs dry. The valve device has a float ball arranged in a cage and floating in the bottom chamber in the case of sufficient water level so as to pump from below upwardly toward the downwardly located outlet of the auxiliary chamber and thereby constantly closing the same. Only in the case of a very low water level in the bottom chamber and therefore faulty buoyancy for the float ball it falls due to gravity force so that the outlet of the auxiliary chamber is released and thereby a connection is produced with the bottom chamber. Thereby the pump now can aspirate the unfiltered water from the aquarium tank through the auxiliary chamber and through its outlet into the bottom chamber to prevent a dry running. The auxiliary chamber with the valve device forms in this filter an emergency device which normally does not operate and has nothing to do with the desired alternating lifting-lowering operation.
Another filter is disclosed in the German document DE-PS 27 00 030 which also operates as an alternating lifting-lowering filter, but however is formed not in the same way. This filter is connected with the aquarium tank through a supply conduit. It has only one filter compartment. A bottom chamber is formed in the filter housing under the filter compartment, and a reverse U-shaped conduit with a free tubular end opens into the bottom chamber. A pump is provided in the conduit and aspirates water accumulated there from the bottom chamber to supply the water into the tank through a return conduit leading toward the aquarium tank. For safety reasons for the case of stoppage of the filter compartment, a bypass conduit is provided between the space located above the filter compartment, where the supply is performed, and the bottom chamber. Therefore with the clogged filter compartment, the upwardly supplied water can flow unfiltered through the supply conduit downwardly into the bottom chamber. During aspiration of the water from the bottom chamber through the open end of one leg of the U-shaped structure, the water level in the filter compartment lowers downwardly. The discharge quantity per unit time is greater than the supply quantity per unit time. Because of this device, a lifting-lowering operation is performed. The filter is however complicated as to the device for actuating the lifting-lowering function, since the reverse U-shaped tube connected with the pump extends through the filter mass in the filter compartment with both legs. In addition the filter mass in the filter compartment is also pierced through by the bypass conduit with concomitant problem arising when the one leg of the U-shaped structure extends through the bypass conduit.